The "psychosine hypothesis" will be further explored as a plausible biochemical pathogenetic mechanism in globoid cell leukodystrophy (GLD). In vitro toxicity of psychosine (galactosylsphingosine) on UDP-gal: ceramide galactosyltransferase will be examined in detail using microsome-bound and solubilized enzyme preparations. The effects of psychosine on formation of myelin and its constituents will be tested using myelinating CNS cultures. Apparent enzymatic differences between the human and canine GLD will be compared by studying the electrofocusing patterns of galactosylceramidase in canine fibroblasts and serum, which do not show the galactosylceramidase deficiency demonstrable in solid tissues and leukocytes. Also using the canine model, we will explore the bichemical basis for the regional differences in susceptibility within the white matter by examining the regional levels of galactosylceramidase and galactosylceramide turnover. In order to gain insight into the relative role of the two genetically distinct beta-galactosidases in in vivo hydrolysis of lactosylceramide, uptake, exclusion, and hydrolysis of tritiated lactosylceramide will be studied with fibroblasts from normal, GLD, and GM1-gangliosidosis patients. The possible interrelationship between purified sphingomyelinase A and B will be examined by immunological techniques. Similarly, the interrelationship between the acidic and the magnesium-dependent neutral sphingomyelinases will be explored immunologically. These basic studies should help our study on the enzymatic basis of different Niemann-Pick (N P) disease phenotypes. Proteins will be sought in N-P tissues that corss-react with antibodies against normal sphingomyelinases. If this is successful, attempts will be made to isolate mutant sphingomyelinase from N-P tissues. Exploration into the genetic defect of adrenoleukodystrophy will continue. Emphasis will be on the metabolism of very long cahin fatty acids. Rat brain and cultured fibroblasts will be edtensively utilized for both in vivo and in vitro studies.